The demand for high component density on contemporary printed circuit boards, particularly in the case of boards designed for computer applications, has resulted in a substantial effort directed towards the miniaturization and subminiaturization of discrete electrical components mounted on such boards. In the case of conventional components, such as resistors and capacitors, such elements, once installed by soldering, are essentially permanent, requiring removal from the circuit board only in the event of component failure. This happens only rarely; however, subminiature fuses are also mounted on such boards, and their occasional replacement is to be expected.
Prior to the present invention, fuses used on printed circuit boards had flexible leads or had rigid plug-in terminals which were plugged into sockets and anchored therein by solder. Where they had flexible leads, they were either soldered to terminals on the board or were bent into a parallel confronting relationship and plugged into socket terminals in the printed circuit board.
Surface mounting of electrical components, like capacitory resistors, but not fuses, in printed circuit boards is becoming popular. These components are provided with terminals on the bottom surfaces thereof, which are placed into facial contact with terminal pad areas on the printed circuit boards. Cylindrical fuses with cylindrical end caps have not heretofore been surface mounted or clip-mounted on printed circuit boards since the leads of these fuses presumed that they could not be so mounted.
The present invention was developed to mass produce a new type of subminiature cylindrical cartridge fuse where the fuse has no leads and so is more compact than the cartridge fuses heretofore used on printed circuit boards, and can be surface mounted on terminal pads or received clips on the circuit board. The cup-shaped end caps of these fuses can be received in terminal clips or are seated on terminal pads on the printed circuit board and soldered thereto.
In the normal course of manufacture of larger cartridge fuses, a fuse filament is mounted within an insulating tube and folded over the outer ends thereof, whereupon the generally cup-shaped conducting terminal-forming end caps are pressed over the ends of the tubes to anchor the fuse element in place, at the same time making electrical contact thereto. A subsequent heating operation causes a solder bonding of the ends of the fuse element to pre-tinned interior regions of the terminal caps, completing the assembly. In the case of cartridge fuses previously so made, such assembly operations are relatively easy and straightforward. In the case of subminiature fuses which are to have leadless end caps of a diameter on the order of 0.075 inches, the problem of orienting the end caps prior to press-on assembly over the ends by automatic machinery has proven to pose a formidable problem.
There remains a need for a simple and inexpensive way of orienting and aligning such subminiature end cap terminals during the assembly process, and in particular there remains a need for such a method which is compatible with automatic fabrication techniques. To the applicant's knowledge, to date there has been no satisfactory method for accomplishing this in a reliable and inexpensive way.